An Experimental Investigation of Wettability Alteration on Carbonate Rocks by Surfactant

The outcrop of carbonate reservoirs is generally water-wet. However, in many cases, water film stability depending on surface charge between oil/water and rock/water interfaces is collapsed and the wetting condition changes from water-wet to oil-wet or intermediate wettability. The main cause of this phenomenon is resulted from the adsorption of some fatty acids in oil phase. Thus, due to the negative amount of capillary pressure, spontaneous imbibitions will not accomplish and consequently ultimate oil recovery will decrease. The utilization of surfactants is one of the available routes for wettability alteration of reservoir rock from oil-wet into water-wet. These materials can diffuse into water/oil or rock/oil interfaces through interfacial reduction and can consequently cause the wettability alteration of the trapped oil. Thus studying wettability alteration mechanism using surfactants has been emphasized by recent researchers. This work focuses on presenting a process mechanism, which has a direct effect on surfactants behavior in oil field usage by using analysis techniques such as zeta potential, TGA, and the injection of surfactant solutions in porous media via core flooding apparatus. The results show that cationic surfactants have the greatest effect on wettability alteration at above critical micelle concentration (CMC) because of the electrostatic attraction between surfactant and adsorbed fatty acids in crude oil, whereas anionic and nonionic surfactants have less performance in the wettability alteration of carbonate rocks.